1. Field of the Invention
This invention relates to a sense amplifier circuit for stably amplifying very small voltage differences, for example, in a semiconductor memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory) and, more particularly, to a current sensing type sense amplifier circuit for a memory.
2. Description of Related Art
Sense amplifier circuits are generally used to amplify very small voltage differences in a memory device. This type of the sense amplifier circuit has been disclosed in various literature (such as a publication entitled "A 7 ns 140 mW 1 Mb CMOS SRAM with Current Sense Amplifier" 1992 IEEE International Solid-State Circuits Conference; pp. 208 and 209 authored by Katsuro Sasaki et al.)
Such a conventional sense amplifier, however, has the following problems. Lack of uniformity in manufacturing processes or positional shifts of masks may cause a transistor's parameters to deviate among many memory cells in a produced memory. The voltage or current given to the data lines therefore varies, so that the sense amplifiers suffer from output deviations. In general, a great number of sense amplifier circuits are placed on a memory chip. When each sense amplifier circuit uses many elements such as transistors, all the sense amplifier circuits tend to occupy a relatively large total mount of area on the memory chip and make it difficult to obtain a higher density memory. Moreover, today's memory standards require low power consumption.